I am making a unit converter for a homework assignment, and I am using abbreviations for the various units of measurement as variable names, but when I try to define 'in' as a variable, it thinks I mean to use the word 'in' as if I wanted to say 'for x in y' or something like that, and I get the following error:
File "unit_converter-v1.py", line 13
in = 12
SyntaxError: invalid syntax
in is a python keyword, so no you cannot use it as a variable or function or class name.
See https://docs.python.org/2/reference/lexical_analysis.html#keywords for the list of keywords in Python 2.7.12.